The present invention relates to a method for metallizing semiconductor components in which aluminium is used. In particular in the case of products in which the process costs play a big part, such as e.g. solar cells based on silicon, a cost advantage can be achieved with the invention. In addition, the present invention relates to the use of the method, for example in the production of solar cells.
In the case of the crystalline solar cells produced for the most part nowadays, the rear-side contact is achieved by alloying an aluminium-containing screen printing paste into the silicon material. The paste is hereby heated briefly above the melting point thereof and subsequently forms a continuous aluminium layer which ensures the transverse conductivity of the rear-side metallization. Furthermore, the aluminium is mixed with the silicon and forms a eutectic which improves the electrical properties of the solar cell rear side.
This procedure in fact offers good electrical conductivity but the electrical and optical properties are only moderate. Furthermore, the thermal loading which is required when alloying in the paste represents a limitation with respect to the further optimisation possibilities of a solar cell since, for example, not all subsequent processes are temperature-stable.
A significant improvement in the optical and electrical properties can be achieved if the rear side is passivated firstly with a dielectric layer made of e.g. silicon oxide, silicon nitride or amorphous silicon. The rear side is subsequently metallized with an aluminium layer. This is applied as standard by vacuum methods, such as e.g. evaporation coating or sputtering.
In the case of these methods, problems arise above all as a result of the vacuum, there being understood in this respect pressures of <1 mbar. The production of the vacuum (i.e. evacuating the process chamber) extends the process times and leads to high costs. In addition, specific substances which would gas out in the vacuum cannot be coated in the vacuum. A third point is the impossibility of depositing layers deposited in the vacuum specifically at defined positions, i.e. an increased material consumption and also pollution of the process chamber arises, which in turn can lead to an impairment in quality of the coated components.
When using a dielectric layer, the aluminium layer can subsequently be contacted with the silicon via various methods, inter alia also via an LFC method.
It is the object of the present invention to make possible an economical and rapid method for coating a surface of a semiconductor with aluminium at low process temperatures. This object is achieved by the method having the features of patent claim 1. A use according to the invention of the method is indicated in patent claim 13. The respective dependent claims thereby represent advantageous developments.